So, I have tried my Onboard GPU, and everything works like a charm.
But when I set my PC to PCI and make it run on my GPU, I either get no screen at all (Black screen), or it freezes at Windows Logo screen when logging in, or I do get in, but everything is black and white and set to 800 x 680 resolution.

BTW, I just got a brand new Mobo, CPU and Ram, and after that, I have had this major trouble with my GPU.

Titan

When you swapped motherboards, did you re-install Windows? If not, do that, and check for a newer BIOS for the motherboard. If anything is overclocked, set to stock speeds. Re-seat the components also.

Yes, I have reinstalled Windows several times by now.
I have used the disc that comes along with the Mobo, isn't that sufficient to make it up to date?
How do I know if anything is overclocked?
Components reseated multiple times aswell.

Titan

Yes, I have reinstalled Windows several times by now.
I have used the disc that comes along with the Mobo, isn't that sufficient to make it up to date?
How do I know if anything is overclocked?
Components reseated multiple times aswell.

No, the disk is probably several versions behind the current drivers, you would want to download the drivers from the vendor support site.

If you did not overclock the system then it's not overclocked. Odd that you would buy such a high end CPU unlocked and don't know about overclocking. Normally people that buy a K model CPU do so for overclocking.

What is your power supply brand and model? Test the video card in another system to see if the issue is a bad card.